Resistance change memory device having a variable resistance element formed of a first and second composite compound for storing a cation

ABSTRACT

A resistance change memory device including: a semiconductor substrate; at least one cell array formed above the semiconductor substrate, each memory cell having a stack structure of a variable resistance element and an access element, the access element having such an off-state resistance value in a certain voltage range that is ten times or more as high as that in a select state; and a read/write circuit formed on the semiconductor substrate as underlying the cell array, wherein the variable resistance element comprises a recording layer formed of a first composite compound expressed by A x M y O z  (where “A” and “M” are cation elements different from each other; “O” oxygen; and 0.5≦x≦1.5, 0.5≦y≦2.5 and 1.5≦z≦4.5) and a second composite compound containing at least one transition element and a cavity site for housing a cation ion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a resistance change memory device, whichstores a resistance value determinable by a resistance change of memorymaterial in a non-volatile manner.

2. Description of the Related Art

Recently, there have been proposed some memory devices having variableresistance elements. One of such the memory devices is known as a phasechange memory which uses phase transition between an amorphous state anda crystalline state of a memory material (for example, U.S. Pat. No.6,314,014B1). In such the phase change memory device, by controlling thecurrent of a chalcogenide cell, reversible switching may be performedbetween a crystalline state (i.e. low resistance state) and an amorphousstate (i.e. high resistance state). Apply a large current to a cell soas to cause the cell chalcogenide to be melted, then rapidly cool downit, and a low resistance state may be written. Anneal the chalcogenidein such a degree as to crystallize it without melting, and a highresistance state may be written. Therefore, it is possible to obtain anelectrically rewritable non-volatile memory device.

Other programmable resistance memories have been proposed as includingprogrammable resistances switchable between a low resistance state and ahigh resistance state by reversing the polarity of voltage application.One of these has an ion conductor formed of a chalcogenide containingmetals (for example, U.S. Pat. No. 6,418,049B1), and another one has apolymer in which conductive particles are dispersed (for example, U.S.Pat. No. 6,072,716). In these memories, dendrite growth and retractionthereof in a solid by voltage application are used. In order to write alow resistance state into a cell, a voltage is applied between the anodeand cathode of a cell in such a polarity that the anode is positive. Asa result, a dendrite grows from the cathode to reach the anode, wherebythe cell becomes to be a low resistance state. A reverse voltageapplication retracts the dendrite to cause the cell to be in a highresistance state. Such the resistance change is reversible, and the lowresistance state and the high resistance state may be stored in anon-volatile manner.

It has been suggested that it is possible to achieve an electricallyrewritable non-volatile memory with a high density by use of such theprogrammable resistance. However, there has not been proposed a detailedconfiguration of a cell array and a read/write circuit thereof. In orderto achieve a practical non-volatile memory with a high density and ahigh performance, how to combine the programmable resistance with whatkinds of switching devices for constituting a cell array, how toconstruct the read/write circuit in communication with the cell array,and the like become important technical issues.

SUMMARY OF THE INVENTION

A resistance change memory device in accordance with an aspect of theinvention including:

a semiconductor substrate;

at least one cell array, in which memory cells are arranged, formedabove the semiconductor substrate, each the memory cell having a stackstructure of a variable resistance element and an access element, thevariable resistance element storing a high resistance state or a lowresistance state in a non-volatile manner, the access element havingsuch an off-state resistance value in a certain voltage range that isten times or more as high as that in a select state; and

a read/write circuit formed on the semiconductor substrate as underlyingthe cell array for data reading and data writing in communication withthe cell array, wherein

the variable resistance element includes a recording layer formed of afirst composite compound expressed by A_(x)M_(y)O_(z) (where “A” and “M”are cation elements different from each other; “O” oxygen; and0.5≦x≦1.5, 0.5≦y≦2.5 and 1.5≦z≦4.5) and a second composite compoundcontaining at least one transition element and a cavity site for housinga cation ion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining the principle of data write for aprogrammable resistance memory element according to an embodiment of thepresent invention.

FIG. 2 is shows a basic cell array and a voltage application modethereof for a selected cell according to the embodiment.

FIG. 3 shows another voltage application mode for the selected cell inthe basic cell array.

FIG. 4 shows a read/write voltage relationship for a unit cell.

FIG. 5 shows a cell characteristic for explaining a write principle.

FIG. 6 shows a cell characteristic for explaining a read principle.

FIG. 7 shows a layout of a three-dimensional cell array according to theembodiment.

FIG. 8 is a sectional diagram as taken along line I-I′ of thethree-dimensional cell array shown in FIG. 7.

FIG. 9 is a sectional diagram of another three-dimensional cell array.

FIG. 10 shows an equivalent circuit of the three-dimensional cell array.

FIG. 11 shows a resistance distribution of memory cells.

FIG. 12 shows a resistance distribution of the three-dimensional cellarray according to the embodiment.

FIG. 13 shows a pair cell configuration method according to theembodiment.

FIG. 14 is a diagram showing operational wave forms for explanation ofdata read according to the embodiment.

FIG. 15 is a diagram showing operation wave forms for explanation ofdata write according to the embodiment.

FIG. 16 a diagram showing operation wave forms for explanation of datawrite for two pair cell in adjacent two cell arrays.

FIG. 17 shows another pair cell configuration method.

FIG. 18 is a perspective view showing a stack structure of thethree-dimensional cell array and a read/write circuit thereof accordingto the embodiment.

FIG. 19 is a cross-sectional diagram showing the interconnectionrelationship between bit lines of the cell array and the read/writecircuit.

FIG. 20 is a cross-sectional diagram showing the relationship betweenword lines and the read/write circuit.

FIG. 21 is a diagram showing a layout of the read/write circuit.

FIG. 22 is a diagram showing the word line select circuit portion of theread/write circuit.

FIG. 23 is a diagram showing the bit line select circuit portion of theread/write circuit.

FIG. 24 shows a main portion layout of the transistor circuit shown inFIGS. 22 and 23.

FIG. 25 is a perspective view of the cell array state after the bit lineformation.

FIG. 26 is a perspective view of the cell array state after the memorycell formation on the bit lines.

FIG. 27 is a perspective view of the cell array state after the wordline formation.

FIGS. 28A to 28C are cross-sectional views showing the word line formingprocess.

FIG. 29 is a diagram showing a variable resistance element in accordancewith another embodiment.

FIG. 30 shows a modified element structure.

FIG. 31 shows a preferable element structure.

FIGS. 32A to 32C each shows an element structure with a heater(s)attached.

FIGS. 33 to 41 show compound examples usable in this embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a principle configuration of a programmable resistance(variable resistance) VR used in the present invention. The programmableresistance VR is formed of a resistance film 3 as being a memorymaterial, and cathode, anode electrodes 1, 2 that sandwiches theresistance film 3.

The resistance film 3 is, for example, an ion conductor (solidelectrolyte) formed of a chalcogenide containing metal ions such assilver, copper and the like. For example, Ge—S, Ge—Se and the like maybe used as the chalcogenide. When the resistance film 3 is formed of theabove-described chalcogenide, the electrodes 1, 2 are also formedcontaining silver therein.

The resistance film 3 stores, for example, a high resistance state as adata “0” and a low resistance state as a data “1”. In this programmableresistance VR, apply a positive anode-cathode voltage (V_(AK)>0) that isover a threshold value, and a data “1” will be written. Apply a negativeanode-cathode voltage (V_(AK)<0) that is over a threshold value, and adata “0” will be written. When “1” data is written, as a result of thevoltage application of V_(AK)>0, a conductive dendrite 4 grows from thecathode electrode 1 toward the anode electrode 2 in the resistance film3 as shown in FIG. 1. When the dendrite 4 reaches the anode electrode 2,the high resistance state (data “1”) is obtained. Apply a reversevoltage, and the dendrite 4 is retracted or broken, whereby the lowresistance state (data “0”) is obtained. Such the low resistance stateand the high resistance state may be statically held as far as a voltageis not applied over the threshold.

It should be appreciated that the resistance film 3 may be formed of apolymer in which conductive particles are dispersed (for example, carbonpolymer in which carbon black particles are dispersed). In this case, alow resistance state and a high resistance state are reversibly writtenbased on the same principle as above-described.

The principle of the above-described memory operation is based on amechanism as described below. An ion conductor or a polymer isamorphous, and potential barriers are formed at random and staticallytherein. In addition, in the potential barrier distribution, potentialvalleys are formed continuously from the cathode to the anode. Dispersesome kinds of metals in such a solid material, and it is possible tomove metal ions along the potential valleys due to electric fieldapplication. When a voltage is applied in such a polarity that anodeside is positive, metal ions move toward the cathode, and then metaldendrite grows from the cathode electrode. Reverse the polarity of theelectric field, and the metals in the dendrite is charged and separatedfrom the dendrite, then move toward the cathode along the potentialvalleys. As a result, the dendrite may be retracted.

Data read of such the programmable resistance VR may be performed bycurrent monitoring when a voltage is applied to the programmableresistance VR with such a degree that dendrite growth and retractionthereof do not occur.

Alternatively, it is possible to use a large read voltage without datadisturbance in a condition that it has such a polarity as to acceleratethe data “0”, “1” state.

FIG. 2 shows a basic cell array of a programmable resistance memory inaccordance with an embodiment, with respect to a 3×3 cell matrix. Aplurality of first wirings (hereinafter, bit lines BL) are provided inparallel, and a plurality of second wirings (hereinafter, word lines WL)are provided to cross the bit lines BL. Memory cells MC are laid out atthe respective crossing points of these word lines WL and bit lines BL.The memory cell MC is a series-connection circuit of a programmableresistance VR and a Zener diode ZD. The anode of Zener diode ZD isconnected to word lines WL.

In a non-select state, the bit lines BL are held at a high level voltageV_(H), and the word lines WL are held at a low level voltage V_(L). Inthis state, Zener diodes ZD are in a reverse-biases state and thus arein an off-state. FIG. 2 shows such a case that cell selection isperformed by use of a forward-bias characteristic of the Zener diode ZD.

Therefore, in order to select a cell MC, which is surrounded by brokenlines, let a selected word line WL at the high level voltage V_(H), andlet a selected bit line BL at the low level voltage V_(L); whereby, atthe selected cell, its diode ZD becomes forward-biased to be in anon-state, and a voltage is applied to one programmable resistance VR.

FIG. 3 shows such a case that a reverse bias is applied to theprogrammable resistance VR in the same cell array shown in FIG. 2. Inthis case, breakdown of the Zener diode ZD is used. Zener breakdown isgenerated by band to band tunnelling of the diode junction, andbreakdown start voltage (Zener voltage) VZ may be controlled by theimpurity concentration of the diode. As similar to FIG. 2, in anon-select state, the bit lines BL are held at a high level voltageV_(H), and the word lines WL are held at a low level voltage V_(L). Inorder to select a cell MC, which is surrounded by broken lines, let aselected word line WL at a low level voltage V_(LL) lower than V_(L),and let a selected bit line BL at a high level voltage V_(HH) higherthan V_(H) (for example, V_(LL)=V_(L)−Δ, V_(HH)=V_(H)+Δ, where Δ is avoltage level variation); whereby, at the selected cell, a largebackward bias is applied to the diode ZD, thereby causing it breakdown.

As a result, a voltage with a polarity opposite to that in FIG. 2 may beapplied to one programmable resistance VR.

The above-described level relationship is an example. For example, inFIG. 2, although the non-selected bit lines and selected word line areset at the same high level voltage V_(H), and non-selected word linesand selected bit line are set at the same low level voltage V_(L), it isnot necessary to use the same levels in these cases. With respect to thevoltage variation Δ used in the select mode in FIG. 3, it is notnecessary to use the same value for the bit line and word line.

In this embodiment, the cell selection method, in which the forward biascharacteristic of the diode is used as shown in FIG. 2, is used for “0”data write and data read; and the cell selection method, in which thebackward breakdown of the diode is used as shown in FIG. 3, is used for“1” data write. Giving attention to one memory cell, read and writecharacteristics will be described in detail, referring to FIGS. 4 and 5.

FIG. 4 shows a relationship between a read voltage Vr, a write voltageVw and a voltage of Zener diode ZD. Programmable resistance VR isconnected with such a polarity that anode (A) thereof is connected tothe bit line BL. The read voltage Vr and write voltage Vw are onesbetween word line WL and bit line BL.

FIG. 5 shows characteristic changes of the programmable resistance VR inaccordance with write operations by use of a voltage (V)-current (I)characteristic of the diode ZD and a V-I characteristic (i.e., loadline) of the programmable resistance VR. In the first quadrant, aforward-bias characteristic curve 50 of the diode ZD is shown. This isexpressed as follows; I=I₀{exp(qV/kT)−1}. The third quadrant showsbackward-bias characteristic curves 51 a, 51 b of the diode ZD. In thenon-select state, the voltage applied to the cell is V_(L)−V_(H), thusthe diode ZD is held at a high-impedance off-state on the curve 51 a

In the first quadrant of FIG. 5, “0” write operation is performed asfollows. Apply a write voltage VW(0)=V_(H)−V_(L) in such a conditionthat Zener diode ZD becomes to be an on-state, and the cell held in a“1” data state (i.e., low resistive state) 53 is written into a “0” datastate (i.e., high resistive state) 54. In principle, it is possible touse the first quadrant characteristic for “0” writing or for “1”writing.

However, since it is required to use this quadrant for cell data readingas described later, “0” write operation is performed in the firstquadrant. This can be the in other words that the programmableresistance VR is connected with such a polarity that anode (A) thereofis connected to the bit kine BL in the cell array configuration shown inFIGS. 2 to 4. Corresponding with the write voltage application, a loadline 53 of “1” data state changes to a load line 54 of “0” data state,as shown by an arrow, as a result of that the dendrite of theprogrammable resistance is retracted, and resistance value thereofbecomes high.

In order to cause the programmable resistance of “1” data to take placesuch the change, it is required that a voltage higher than a certainlevel is applied to the programmable resistance. Such the level is shownas a “0” write threshold value VT in FIG. 5. VT is a voltage applied tothe programmable resistance VR, and expressed as a negative voltage withreference to Vw(0). If the cross point B1 between the forward biascharacteristic curve 50 of the Zener diode ZD and the load line 53 of“1” data state of the programmable resistance is positioned between theorigin and Vw(0)−VT, “0” write may be done into the programmableresistance. As described above, use the first quadrant for “0” write,and it becomes hard to occur error write to the programmable resistancein a read mode. The reason of this will be described in detail later.

In the third quadrant, “1” write is performed. In this case, apply alarge backward bias, and it may cause the Zener diode breakdown, and itallows of current flowing with an approximately constant voltage. In thedrawing, “1” write operation is shown as follows; when write voltageVW(1)=V_(LL)−V_(HH) is applied as being over the breakdown voltage(Zener voltage) Vz, the programmable resistance VR changes from a highresistive state 56 of “0” data to a low resistive state 55 of “1” data.Load lines 56, 55, which express “0”, “1” states respectively, haveinclinations in correspondence with resistance values.

Therefore, these are in parallel with the load lines 53, 54 in the firstquadrant, respectively. In this case, it is also required forsuccessfully writing to the programmable resistance that a voltagehigher than a threshold value VT is applied to it. If the cross point B2between the breakdown characteristic curve 51 b of the Zener diode ZDand the load line 56 of “0” data state of the programmable resistance ispositioned between the origin and Vw(1)+VT, “1” write may be done intothe programmable resistance. Voltages V_(LL), V_(HH) and the like areselected in such a condition that sufficiently high voltage is appliedto the programmable resistance.

If the resistance value of “1” data written programmable resistance istoo low, a large current will flow through the Zener diode ZD, therebycausing it thermal breakdown.

Therefore, it is required to give attention to the current value.Corresponding to some cases, it will be necessary to dispose a currentlimiter.

If the third quadrant is used for “0” writing, there is not any fear ofthermal breakdown, because the load line variation due to writing is insuch a direction that the current value decreases. In this case,however, since it is required to use the first quadrant for “1” writing,the possibility of erroneous writing in a read operation is undeniable.

In FIG. 5, voltage variations C1 to C3, which are applied tonon-selected cells during selective writing operation for the cell arrayshown in FIGS. 2 and 3, are shown. C1 is a voltage variation ofnon-selected cells along the selected bit line and selected word lineduring “0” data writing shown in FIG. 2; C2 is a voltage variation ofnon-selected cells along the selected bit line and selected word lineduring “1” data writing shown in FIG. 3; and C3 is a voltage variationof non-selected cells along the selected bit line and selected word linein such cases that during a “1” writing operation for a cell as shown inFIG. 3, “0” writing is performed for another cell as shown in FIG. 2.

Such the cases are not used in the above-described write operation. Itis required that these voltage variations C1 to C3 are insufficient tobreak data of the non-selected cells. Therefore, it is necessary forselecting the values of V_(H), V_(HH), V_(L) and V_(LL) in such acondition that the voltage variations do not cause the Zener diodes ofthe non-selected cells to be forward-biased to turn on, or do not causethose breakdown in the backward-bias direction.

FIG. 6 shows a characteristic of read operation which is performed byuse of the first quadrant, with the “0” write characteristic (shown bybroken lines). Since it is necessary to preform read operations with alow voltage necessary for preventing the cells from erroneous write, theread operations in accordance with this embodiment are performed in thefirst quadrant as similar to “0” write. For example, in a read mode, thehigh level voltage V_(H) is applied to a selected word line, and a lowlevel voltage VLr, which is higher than V_(L), is applied to a selectedbit line. At this time, detect a current difference or a voltagedifference between crossing points S0 and S1 of the forward-biasedcharacteristic curve 50 of the Zener diode and the load lines 58, 57 of“0”, “1” data by a sense amplifier, and read data may be determined.

In the above-described read operation, it is required to prevent thecell from erroneous write due to the read voltage application. As shownin FIG. 6, as far as that the voltage applied to the programmableresistance is set at lower than the threshold value VT in the “1” dataread operation, no erroneous writes occur. In FIG. 6, in the “0” dataread operation, a voltage slightly higher than the threshold value VT isapplied to the programmable resistance. However, this becomes a “0”write mode. That is, a “0” read operation becomes as it is a “0” rewriteoperation, thereby having nothing to do with erroneous write.

As previously described, it is possible to use the first quadrant for“1” data writing in principle. However, in such the case, a “0” readoperation becomes a weak “1” write mode. To avoid such the mode, it ispreferable to use the first quadrant for “0” write operations.

As described above, in the read scheme of FIG. 6, as far as that thecrossing point S1 for “1” data reading is in the voltage range betweenVr and Vr−VT, no erroneous writes occur. In other words, it is possibleto set the read voltage Vr without considering the crossing point S0 for“0” data reading. Therefore, a sense margin and a sense speed may beimproved. Supposing that the third quadrant is used for data readoperation, since Zener voltage Vz is approximately constant, it isdifficult to obtain a sense margin necessary for preventing theerroneous write.

As above-explained, in this embodiment, Zener diode is used as an accesselement for applying voltages to the programmable resistance in oppositepolarities, whereby the forward bias characteristic and the backwardbias breakdown characteristic thereof may be used. In the backward biascharacteristic, there is a voltage region, in which a resistance valueis regarded as being approximately infinite, under Zener voltage Vz.

This is an important characteristic required for the access element ofthe programmable resistance. In general, it is required of the accesselement to have such an off-state resistance value in a certain voltagerange that is ten times or more as high as that in a select state.

In consideration of this, it should be appreciated that other accesselements, for example, a PN junction diode, a Shottky diode and thelike, may be used as far as that they are held in a high-resistiveoff-state in a certain voltage range.

So far, the configuration of the basic cell array and the principle ofthe data read/write operation have been explained. In this embodiment, athree-dimensional cell array structure in which a plurality of cellarrays are stacked above a semiconductor substrate is utilized. Such athree dimensional cell array will be explained below.

FIGS. 7 and 8 shows a layout and a cross section along I-I′ line thereofof a three-dimensional (3D) cell array including four-layer stacked cellarrays MA0 to MA3. In these figures, the same reference numerals areused at the same parts or components in the respective cell arrays,which numerals are distinguished between the cell arrays by addition ofsuffixes “a”, “b”, “c” and “d” thereto, and also distinguished betweenthe shared portions of each two cell arrays by addition of suffixes“ab”, “bc” and “cd”.

A silicon substrate 10 is covered with an insulator film such as asilicon dioxide film. Above the substrate, a plurality of bit lines (BL)12 a are arranged in parallel with each other. Pillar-type memory cellsMC are arranged on each bit line 12 a at a certain pitch, each of whichhas a variable resistance element VR and a Zener diode ZD stackedthereon. Word lines (WL) 18 ab are formed to commonly connect the upperends of the memory cells MC in a direction perpendicular to the bitlines 12 a, whereby first cell array MA0 is formed.

As above-described, the variable resistance element VR is written into a“0” state by applying a high level voltage to the word line WL and a lowlevel voltage to the bit line BL to cause it to be forward-biased.Therefore, the variable resistance element VR is disposed with such apolarity that anode and cathode thereof are to be connected to the wordline WL and bit line BL, respectively. This is the same for every cellarrays stacked.

In detail, the memory cells MC are formed by patterning laminated layershaving variable resistance element layer 13 a, an ohmic electrode 14 a,an n+-type silicon layer 15 a and a p+-type silicon layer 16 a. Thevariable resistance element layer 13 a is, as shown in FIG. 1, formed ofan ion conductor containing a specified metal or a polymer sandwiched byanode and cathode electrodes. An interlayer dielectric film 17 is buriedaround the memory cells MC to planarize the cell array MA0.

Second cell array MA1 is formed to share the word lines (WL0) 18 ab withthe first cell array MA0. In detail, pillar-type memory cells MC arearranged on each word line 18 ab at a certain pitch, each of which isformed by patterning the laminated films of an p+-type silicon film 16b, an n+-type silicon film 15 b, an ohmic electrode 14 b and a variableresistance element film 13 b to have a stacked structure of a Zenerdiode ZD and a variable resistance element VR. The cell layout is thesame as that of the first cell array MA0. Bit lines (BL1) 12 ab arepatterned to commonly connect the variable resistance element layers 13b arranged along a direction perpendicular to the word lines 18 ab. Aninterlayer dielectric film 19 is buried around the memory cells MC toplanarize the cell array MA1.

The stacked structure of third and fourth cell arrays MA2 and MA3 isperiodically formed as similar to the first and second cell arrays MA0and MA1. Bit lines (BL1) 12 bc are shared with the second cell array MA1and the third cell array MA2. The third cell array MA2 and the fourthcell array MA3 shares the word lines (WL1) 18 cd with each other. Bitlines (BL0) 12 a of the lowest cell array MA0 and bit lines (BL3) 12 dof the uppermost cell array MA3 are independently prepared,respectively. Although the cross section along II-II′ line of FIG. 7 isnot shown, the memory cells MC are disposed on the continuously formedword lines WL at the same pitch as on the bit lines on this crosssection.

As shown in FIG. 7, the bit lines BL and word lines WL of each cellarray are formed with such a pattern that these are rotated by 90° eachother, and memory cells MC are sandwiched therebetween at the respectivecrossing points.

For example, the word lines WL and bit lines BL are formed with aline/space=1F/1F, where F is the minimum device feature size, therebyachieving the unit cell area of 4F2. In order to form such thestructure, it is possible to use in the patterning process of the memorycells MC two exposures with an exposure mask used for patterning theword lines or the bit lines. In detail, in the lithography process forthe laminated layers used for memory cells, exposures are performed attwice with an exposure mask in such a manner that the mask is rotated by90° between the respective exposure steps. Then, etch the laminatedlayers so as to remain overlap portions at the two exposure steps, andit is able to dispose the memory cells MC at the respective crossingportions of the bit lines BL and the word lines WL.

In FIG. 8, the variable resistance element layers 13 are disposed onlyat the cross portions of the bit lines BL and the word lines WL. Incontrast to this, in such a case that the leak current of the variableresistance element layer 13 is negligible small, the variable resistanceelement layer 13 may be remained without patterning, as shown in FIG. 9.In this case, the sandwiched portions between the diode ZD and the bitlines or the word lines within the variable resistance element layer 13materially function as the variable resistance elements VR.

FIG. 10 shows a three-dimensional equivalent circuit of the 3D cellarray formed as above-described. In order to prevent the bit lines frommutual interference, each two bit lines constitute a pair, and anotherbit line is disposed between the pair of bit lines. BL00, /BL00, BL01,/BL01, . . . are bit line pairs of the first cell array MA0; BL10,/BL10, BL11, /BL11, . . . are shared bit line pairs between the secondand third cell array MA1 and MA2; and BL20, /BL20, BL21, /BL21, . . .are shared bit line pairs between the third and fourth cell array MA2and MA3. Further, WL0 (WL00, WL01, . . . ) are shared word lines betweenthe first and second cell arrays MA0 and MA1; and WL1 (WL10, WL11, . . .) are shared word lines between the third and fourth cell arrays MA2 andMA3.

In the above-described 3D cell array in which many memory cells areintegrated, variation of cell characteristics gets into trouble. Indetail, since the resistance value of the variable resistance element VRis determined by dendrite growth and retraction thereof, it is varieddue to a history thereof, environment and the like.

FIG. 11 schematically shows a distribution of the resistance values ofdata “0”, “1”. If there is no overlap region, as shown in FIG. 11,between the resistance values of “0” and “1”, it is able to distinguishbetween “0” and “1” by use of a reference resistance Rref. However, inthe 3D cell array that has numerous cells, it becomes difficult to setsuch the reference resistance Rref. FIG. 12 schematically shows such asituation as above-described. Groups A, B, C and D include nearlydisposed plural cells, respectively.

Give attention to each the group, and it is able to set a referenceresistance Rref. However, with respect to the entire of cell array, itbecomes difficult or impossible.

In consideration of the above-described view points, in this embodiment,nearly disposed two cells constitute a pair cell for storingcomplementary data therein in such a manner that data “0” is stored inone cell and data “1” is stored in the other cell. Read operation isdone by detecting the difference between cell currents of the two cellsconstituting a pair. By use of this scheme, even if there is a partialoverlap between the high resistive state distribution and the lowresistive distribution in the entire 3D cell array, it is possible toprecisely read/write the cell data.

In FIG. 10, two cell pairs are typically shown as follows: two cellsconnected to a pair of bit lines BL00 and /BL00, respectively, withsharing a word line WL00 in the cell array MA0, being constituted to onepair cell, one of which is a true cell “T-ce110” and the other is acomplementary cell “C-ce110”; and two cells connected to a pair of bitlines BL10 and /BL10, respectively, with sharing a word line WL10 in thecell array MA1, being constituted to another pair cell, one of which isa true cell T-cell and the other is a complementary cell C-cell. Inevery pairs of cells, a positive logic value of a binary data is storedin the true cell, and a negative logic value is stored in thecomplementary cell. Similar pair cells are selected in the cell arraysMA2 and MA3, too. In FIG. 10, cell currents at the respective readselection times are shown by arrows.

Data read/write methods in such the case that two memory cellsconstitute a pair cell will be described in detail bellow. FIG. 13 showstwo pair cells in two cell arrays disposed adjacent up and down to havea shared word line WL. Data read operations for these two pair cells maybe simultaneously performed by use of operation waveforms as shown inFIG. 14. In a non-select mode, V_(H)−V_(L) between the bit lines and theword lines is a hold voltage which holds the memory cells in such anon-select state that diodes thereof are backward-biased to be in a highresistive off-state.

In a read selection mode as shown in FIG. 14, a high level voltage V_(H)is applied to the word line WL which is held at a low level voltageV_(L) in a non-select time. At the same time, a low level voltage VLr(>V_(L)) is applied to the bit lines BL0, /BL0, BL1 and /BL1 which areheld at high level voltage V_(H) in the non-select time. In other words,between the selected word line WL and the selected bit line pairs BL0,/BL0 and BL1, /BL1, a read voltage Vr=V_(H)−VLr is applied toforward-bias the selected cells. As a result, cell currents flow in therespective cells as above-explained with FIG. 6. Detect the cell currentdifferences between the pair of bit lines BL0, /BL0, and between thepair of bit lines BL1, /BL1 by sense amps, and cell data of therespective pair cells may be determined. Since each pair cell isconstituted by neighbouring two cells to store complementary data, it ispossible to precisely sense the cell data.

Next, data write operations into pair cells will be described. Althougha pair of cells store a data “0” in one cell and a data “1” in the othercell, “0” and “1” write voltages applied between the word line and thebit line have to be opposite each other as above-described. This meansthat it is impossible to simultaneously write data into the true cell,T-cell, and the complementary cell, C-cell, which share a word line.Therefore, it is required to perform data write operations for a paircell at twice.

FIG. 15 shows waveforms of “0” data writing (i.e., T-cell=“0”,C-cell=“1”) and “1” data writing (i.e., T-cell=“1”, C-cell=“0”) into apair cell. In order to write “0” data, with respect to the bit lineswhich are held at the high level voltage V_(H) in the non-select mode, alow level pulse voltage V_(L) is applied to one of bit line pair, BL0(or BL1), and a high level pulse voltage V_(HH) higher than V_(H) isapplied to the other, /BL0 (or /BL1). A high level voltage V_(H) isapplied to the word line WL in the former half T1 of the above-describedbit line selection period, and a low level voltage V_(LL) lower thanV_(L) is applied to the same in the latter half T2.

As a result, in the former half T1, “0” write voltage,Vw(0)=V_(H)−V_(L), is applied to one cell, T-cell, of the pair cell toforward-bias the diode thereof due to the high level voltage V_(H) ofthe word line WL and the low level voltage V_(L) of the bit line BL0 (orBL1), whereby T-cell is written into a “0” data state. At this time, thevoltage applied to the other cell, C-cell, is V_(H)−V_(HH). Since thediode of C-cell is held at an off-state in this condition, no error dataare written into C-cell. In the latter half T2, “1” write voltage,VW(1)=V_(LL)−V_(HH), is applied to the other cell, C-cell, of the paircell to cause the diode thereof breakdown due to the low level voltageV_(LL) of the word line WL and the high level voltage V_(HH) of the bitline /BL0 (or /BL1), whereby C-cell is written into a “1” data state. Atthis time, the voltage applied to the cell T-cell, in which a data hasbeen written, is V_(LL)−V_(L). Since the diode of T-cell is held at anoff-state in this condition, no error data are written into T-cell.

In order to write “1” data, pull up one of bit line pair, BL0 (or BL1),to the higher level voltage V_(HH) from the high level voltage V_(H),and pull down the other, /BL0 (or /BL1), to the low level voltage V_(L)from the high level voltage V_(H). And, as similar to the “0” writemode, the high level voltage VH is applied to the word line WL in theformer half T1 of the above-described bit line selection period, and thelow level voltage V_(LL) is applied to the same in the latter half T2.

As a result, in the former half T1, one of the pair cell, C-cell, iswritten into a “0” data state because of that diode thereof isforward-biased due to the high level voltage V_(H) of the word line WLand the low level voltage V_(L) of the bit line BL0 (or BL1). In thelatter half T2, the other cell, T-cell, is written into a “1” data statebecause of that the low level voltage VLL of the word line WL and thehigh level voltage V_(HH) of the bit line /BL0 (or /BL1) cause diodethereof breakdown. No erroneous writes occur in both of the former halffor “0” writing and the latter half for “1” writing, as similar to theabove-described “0” writing mode.

As apparent from FIG. 15, “0”, “1” writing into a pair cell may beselected by reversing the voltages applied to the bit line pair, whilethe same voltage is applied to the word line. Therefore, it is able toperform simultaneous data writing into two pairs of cells with a sharedword line.

FIG. 16 shows in detail waveforms of simultaneous data writing into twopair cells, (T-cell0, C-cell0) and (T-cell1, C-cell1), which areneighbouring up and down with a shared word line WL00. The datacombinations of the two pair cells are expresses as four values “00”,“01”, “10” and “11”.

Corresponding to the four values data, in FIG. 16, bit data of T-cell1,C-cell1, T-cell0 and C-cell0 are shown at upsides of the respectivewaveforms. To the respective bit line pairs, (BL00, /BL00), (BL10,/BL10), the high level voltage V_(HH) and the low level voltage V_(L)are applied in correspondence with to-be-written data. The voltagesapplied to the word line WL00 are changed all the same for the four datasuch that the high level voltage V_(H) and the low level voltage V_(L)are applied in the former half and the latter half respectively in thebit line selection period, as similar to that in FIG. 15. By use of suchwaveforms, two pair cells may be simultaneously written.

As apparent from the above-described write operations, it should beappreciated that it is possible to simultaneously access to therespective plural pair cells within the first and second cell arrays MA0and MA1 with shared word lines. Similarly, it is possible tosimultaneously access to the respective plural pair cells within thethird and fourth cell arrays MA2 and MA3 with shared word lines.

In contrast to this, note that it is not allowed to simultaneouslyaccess to the second and third cell arrays MA1 and MA2 with shared bitlines.

Up to the present, it has been explained such a pair cell configurationthat laterally neighbouring two memory cells constitute a pair cell ineach cell array layer in the three-dimensional cell array. However, thepair cell configuration method is not limited this.

As shown in FIG. 17, it is possible to select vertically neighbouringtwo memory cells MC with a shared word line WL so as to constitute apair cell (i.e., a true cell, T-cell, and a complementary cell, C-cell).In this case, the bit lines BL0, BL1 which belong to different cellarrays becomes a pair of bit lines to be connected to the pair cell.

FIG. 18 is a schematic perspective view showing a stacking state of cellblocks 100 and a read/write circuit 200 and interconnectionrelationships therebetween. Each the cell block 100 corresponds to theabove-described 3D cell array with four layers.

A 3D cell array is, when necessary, divided into a plurality of cellblocks 100 with a predetermined capacity. In FIG. 18, two cell blocks100 are arranged in a direction along the bit lines.

As shown in FIG. 18, the read/write circuit 200, which is used for datareading and writing in communication with the cell block 100, isunderlain the cell block 100. The read/write circuit 200 is formed insuch a state that main portion thereof is disposed within a rectangularcell layout region 210 defined on the substrate 10, above which the cellblock 100 is stacked. The cell layout region 210 is defined by twoboundaries A1 and A2 in the direction of the bit lines, and by twoboundaries B1 and B2 in the direction of the word lines.

A group of bit lines BL0 of the first cell array MA0 and a group of bitlines BL2 of the fourth cell array MA3 are drawn to the first boundaryA1 side to be connected to a bit line select circuit 201, which isdisposed along the boundary A1 in the read/write circuit 200, throughvertical wirings (i.e., passages that vertically run to the substrate)101 that are disposed along the boundary A1. A group of bit lines BL1shared by the second and third cell arrays MA1 and MA2 are drawn to thesecond boundary A2 side to be connected to another bit line selectcircuit 202, which is disposed along the boundary A2 in the read/writecircuit 200, through vertical wirings 102 that are disposed along thesecond boundary A2.

The reason why the bit lines BL0 and BL2 are drawn to the same side tobe commonly connected to the bit line select circuit 201 through thevertical wirings 101 is in such a fact that these groups of bit linesare not simultaneously activated. In detail, cell arrays MA0 and MA1 aresimultaneously activated because of these have shared word lines WL0.

As similar to this, cell arrays MA2 and MA3 are simultaneously activatedbecause of these have shared the word lines WL1. However, since the cellarrays MA1 and MA2 share the bit lines BL1, the lower cell arrays (MA1,MA2) and the upper cell arrays (MA2, MA3) are not activatedsimultaneously. The bit line select circuit 201, 202 include bit linedecoders/multiplexers (BL-DEC/MUX).

The word lines WL0 and WL1 are drawn to the third boundary B1 side to beconnected to word line select circuit 208, which is disposed along theboundary B1 in the read/write circuit 200, through vertical wirings 103and 104, respectively, that are disposed along the boundary B1. The wordline select circuit 208 has word line decoders/multiplexers(WL-DEC/MUX).

A central portion of the read/write circuit 200 serves as a global busregion 207, in which I/O data lines and pulse signal lines are disposedcrossing this region in the direction of the word lines. Between thisglobal bus region 207 and the bit line select circuits 201 and 202,disposed are sense amplifier arrays 203 and 204, respectively. Signallines formed at the global bus region 207 are shared by the senseamplifier arrays 203 and 204.

The sense amplifiers in the sense amplifier arrays 203 and 204 areconnected to bit line select circuits 201 and 202 through signal linesdisposed at local bus regions 205 and 206, respectively. Therefore, someones selected from the bit lines BL0 or BL2 by the bit line selectcircuit 201 are connected to the sense amp array 203. Similarly, someones selected from the bit lines BL1 by the bit line select circuit 202are connected to the sense amp array 204.

The I/O data lines and pulse signal lines disposed at the global busregion 207 are drawn to the fourth boundary B2 side of the cell layoutregion 210. Along this boundary B2, disposed is a write circuit (i.e.,write pulse generator circuit) 209 for applying write pulse signals toselected bit lines.

As above-described referring to FIG. 18, bit lines and word lines of thecell arrays are connected to the read/write circuit 200 formed on thesubstrate 10 through the vertical wirings 101 to 104. Practically, thesewirings 101 to 104 are formed of contact plugs buried in interlayerdielectric films formed surrounding the cell array. The structuralexamples of the interconnections are shown in FIGS. 19 and 20.

FIG. 19 shows a connection state between the bit lines and theread/write circuit 200 on a cross-section along the bit lines of thecell array. FIG. 20 shows a connection state between the word lines andthe read/write circuit 200 on a cross-section along the word lines ofthe cell array.

As shown in FIGS. 19 and 20, the read/write circuit 200 has necessarytransistors and metal interconnections formed on an interlayerdielectric film 11 a covering the transistors.

The read/write circuit 200 is covered by an interlayer dielectric film11 b, and the four layered cell arrays are formed thereon. Therefore,the interlayer dielectric films 11 a and 11 b constitute the insulatorfilm 11 shown in FIGS. 8 and 9.

As shown in FIG. 19, the vertical wirings 101, which are used to connectthe bit lines BL0, BL2 drawn toward the boundary A1 of the cell layoutregion 210 to the bit line select circuit 201, are composed of contactplugs 101 a to 101 e buried in the interlayer dielectric films 17, 19,20 and 21. Similarly, the vertical wirings 102, which are used toconnect the bit lines BL1 drawn toward the boundary A2 of the celllayout region to the bit line select circuit 202, are composed ofcontact plugs 102 a to 102 c buried in the interlayer dielectric films11, 17 and 19.

As shown in FIG. 20, the vertical wirings 103, which are used to connectthe word lines WL0 drawn toward the boundary B1 of the cell layoutregion to the word line select circuit 208, are composed of contactplugs 103 a and 103 b buried in the interlayer dielectric films 11 and17. The vertical wirings 104, which are used to connect the word linesWL1 drawn toward the same side as the word lines WL0 to the word lineselect circuit 208, are composed of contact plugs 104 a to 104 d buriedin the interlayer dielectric films 11, 17 and 20.

Although the lowest contact plugs 101 a, 102 a, 103 a and 104 a of thelaminated cell arrays in FIGS. 19 and 20 are connected to metal wiringsof the read/write circuit 200, it is possible to directly connect theseto source/drain diffusion layers of transistors.

FIGS. 19 and 20 show an example in which the contact plugs are formed ofmetal films used for bit lines and word lines. The fabrication stepswill be described later. Additionally, it is appreciated that thecontact plugs may be formed of other metal films different from the bitlines and word lines or polycrystalline silicon films.

One cell block 100 shown in FIG. 18 includes, for example, 512 bit lines(BL) and 128 word lines (WL) for one cell array. As described above, twomemory cells store one bit data in this embodiment. In this case, onecell block has a memory space of 256 columns (Col)×128 rows(Row). Thememory capacity can be increased by increasing the number of cell blocksto be arranged. In order to achieve a high-speed access in such a largecapacitive memory, it is necessary to perform parallel access formulti-bit data.

For example, in order to perform 32-bits parallel access, one cell blockis to be divided into two parts in the word line direction, and into 32parts in the bit line direction, whereby 64 cell units are obtained. Asa result, each cell unit becomes to have a capacity of 32IO×4Col×4Row×4. On the global bus region 207, data lines and pulse signal linesare disposed for 64IO data input/output.

FIG. 21 shows a schematic layout of the read/write circuit 200 withrespect to one cell block 100 shown in FIG. 18 in a case that theabove-described cell block construction is used. On the word line selectcircuit (WL-DEC/MUX) 208 as been disposed at the right side in FIG. 21,disposed are row address (RA) signal lines 301, which vertically run forselecting one each (i.e., upper and lower ones) from 128×2 word lines inthe cell block 100.

The write circuit 209 disposed at the left side in FIG. 21 output pulsesignals with high level voltage V_(HH) and low level voltage V_(L) thatare supplied to selected bit lines in a write mode (see FIG. 15).

Write pulse signal lines (WP) 305 which transfer the write pulse signalsare disposed as to laterally run on the global bus region 207. Inparallel with the write pulse signal lines 305 on the global bus region207, disposed are main data lines 304, on which read out data aretransferred.

One cell unit is selected in one cell block, and cell data of lower twocell layers or upper two cell arrays in each cell unit aresimultaneously activated. Therefore, data lines 304 are prepared for32IO×2=64IO. The write pulse signal lines are the same.

In detail, in a read mode, read data on plural bit lines, which arerespectively selected from the lower two cell arrays (MA0, MA1) or theupper two cell arrays (MA2, MA3) by the bit line select circuits 201 and202, are simultaneously sensed by the sense amp arrays 203 and 204, andthen simultaneously transferred to the data lines 304. In a write mode,write pulse signals, which are to be supplied to plural bit linesrespectively selected from the lower two cell arrays (MA0, MA1) or theupper two cell arrays (MA2, MA3), are output to the write pulse signallines 304 from the write circuit 209, and then transferred to the pluralbit lines respectively selected by the bit line select circuits 201 and202.

On the lower and upper ends of the read/write circuit 200, disposed arethe bit line select circuits 201 and 202, respectively, and columnaddress (CA) signal lines 302 and 303 are disposed to laterally run onthe respective regions.

One of the bit line select circuits, i.e., circuit 201, selects 32 bitline pairs from 512 bit line pairs(=64IO×4 Col) in the upper two cellarrays, and the other selects 32 bit line pairs from 512 bit line pairsin the lower two cell arrays. Therefore, on the respective local busregions 205 and 206, disposed are four pairs of current pass lines BP,/BP for commonly 4-columns (=8 bit lines) data as to cross the regionsof sense amplifier arrays 203 and 204 for applying the pulse signals ofthe pulse signal lines 305 to bit lines selected by the respective bitline select circuits 201 and 202. Additionally, 64 pairs of local datalines DL, /DL for 4 columns data are disposed on the respective localbus regions 205 and 207, and these are connected to the respective senseamps in the sense amplifier arrays 203 and 204.

One circuit portion 310, that are to be connected to 4 Row×2 (=8 wordlines) and another circuit portion 312, that are to be connected to 4Col (=8 bit lines), each being surrounded by a broken line in FIG. 21,are shown in FIGS. 22 and 23, respectively, in detail.

Two multiplexers MUX0 and MUX1 have select gate circuits for selectingthe lower word lines WL0 shared by the cell arrays MA0 and MA1, and theupper word lines WL1 shared by the cell arrays MA2 and MA3,respectively. Eight word lines input to the multiplexer MUX0 in FIG. 22correspond to the word lines WL0 of the lower two cell arrays in FIG.18.

Decoders DEC include decode gates G (G1, G2, . . . ) for selecting oneof 32 cell units. The multiplexer MUX0 has a select gate circuit 401composed of NMOS transistors QN (QN21 to QN24, QN25 to QN28, . . . )that are driven by select signals S10 to S13 so as to select one fromfour word lines. These NMOS transistors QN21 to QN24 and QN25 to QN28are commonly connected to nodes N11 and N12, respectively. To thesenodes N11 and N12, applied is a word line drive signal Vwdrv output froma word line driver circuit 403 through self-boost transistors QN81 andQN82 which are selectively driven by the decode gates G1 and G2.

The word line drive signals Vwdrv is held at the high level voltage VHin the read mode (see FIG. 14), or at the high level voltage VH in theformer half and the low level voltage VLL in the latter half in thewrite mode (see FIG. 15). The gates of transistors QN81, QN81 areconnected to the output nodes of the decode gates G11, G12 though NMOStransistors QN83, QN84 so as to be selectively charged at a high levelby the outputs of the decode gates G11, G12. The word line drive signalVwdrv is applied to a word line WL through on-state NMOS transistorsQN81, QN82.

Since the NMOS transistors QN81, QN82 are configured as transfer gateswhich are to be self-boosted by capacitive coupling between gates andsources therebetween, the word line drive signal Vwdrv, which arechanged between VH and VLL, is transferred to the word line WL withoutvoltage drops.

The multiplexer MUX0 has a reset circuit 402 composed of NMOStransistors QN (QN11 to QN14, QN15 to QN18, . . . ) for holdingnon-selected word lines as being at low level voltage VL=Vss. Themultiplexer MUX1 is composed as similar to the multiplexer MUX0.

A sense amp SA shown in FIG. 23 is one of 32 sense amps in the sense amparray 205 shown in FIG. 21. Four pairs of eight bit lines BL0, /BL0 toBL3, /BL3 connected to the sense amp SA are ones selected from the bitline group BL0 or BL2 shown in FIG. 10. As previously described, sincethe lower two cell arrays MA0 and MA1 and the upper two cell arrays MA2and MA3 are not activated at a time, the sense amplifier SA is commonlyused for the lower cell arrays MA0, MA1 and the upper cell arrays MA2,MA3.

The sense amplifier SA is a CMOS flip-flop type current sensingamplifier with an activating PMOS transistor QP30. Two nodes N1 and N2thereof are directly connected to a pair of ones GBi, /GBi in the globaldata lines 304, respectively. Drains of sensing NMOS transistors QN61and QN62 are selectively connected to data lines DL and /DL through NMOStransistors QN31 and QN32, respectively, that are controlled by a readcontrol signal R to turn-on during a read operation.

Except on the data read time, the nodes N1 and N2 are shorted with eachother by an equalizing transistor QN73. Data lines DL, /DL are connectedto a pair of bit lines selected by the bit line decoder/multiplexerBL-DEC/MUX. Drains of the sensing transistors QN61, QN62 may beselectively set at Vss or at floating states by NMOS transistors QN71,QN72 which are controlled by a clock CLK.

Based on the operations of transistors QN71, QN72, it is possible toapply the low level voltage VLr(=Vss) shown in the waveforms of FIG. 14to selected bit lines and to perform a positive feed-back operation ofthe sense amp SA when cell data are transferred to NMOS transistorsQN61, QN62 in a data sense time.

The bit line decoder/multiplexer BL-DEC/MUX has a select gate 403composed of NMOS transistors QN51 to QN54, and Q55 to Q58 controlled bydecoded signals S20 to S23 for selecting one pair from four pairs of bitlines to connect these to the data lines DL and /DL, respectively.Additionally, the bit line decoder/multiplexer BL-DEC/MUX has a resetcircuit 404 composed of PMOS transistors QP51 to QP54, and QP55 to QP58for holding non-selected bit lines as being at a high level of Vdd.

The pair of data lines DL, /DL are connected to a pair of signal linesWPi, /WPi in the pulse signal lines 305 through NMOS transistors QN41,QN42 that are driven by a write control signal W to turn-on, and throughsignal lines BP, /BP.

In the above-described configuration, when a data read operation isperformed, word lines selected by select gate circuit 403 become “H”,and bit line pairs selected by select gate circuit 403 become “L”. Atthis time, cell currents from the selected complementary cells on theselected bit line pair are transferred to the drains of NMOS transistorsQN61, QN62 of the sense amp SA through data lines DL, /DL and throughNMOS transistors QN31, QN32. During this operation, NMOS transistorsQN71, QN72 are held at an off-state.

Thereafter, clock CLK becomes “H” to turn-on the NMOS transistors QN71,QN72, whereby the drains of the sensing NMOS transistors QN61, QN62 areclamped at Vss. As a result, a differential voltage generated betweenthe nodes N1 and N2 due to the difference of cell currents is positivelyfeeded back to be amplified such that one of the nodes N1, N2 becomesVdd, while the other becomes Vss. Amplified cell data as above-describedis output to the main data lines GBi, /GBi.

In a data write mode, the drive signal Vwdrv, which is at the high levelvoltage V_(H) in the former half and at the low level voltage V_(L) inthe latter half, is applied to a selected word line. Simultaneously,write pulse signals, which are set at combinations among V_(HH), V_(H),V_(L) and V_(LL) corresponding to-be-written data, are applied toselected pair cells through the write pulse signal lines WPi, /WPi,whereby data write operations are performed.

Since one word line is commonly connected to many pair cells, it isrequired for the word line to supply a large current to the pair cells.In consideration of such the current value, it is required to designdrivability of the word line decoder, resistance of the word lineitself, the transistor size, and the like. It should be appreciated thatthe word line multiplexer MUX0 for eight word lines shown in FIG. 22 andthe bit line decoder/multiplexer DEC/MUX for eight bit lines shown inFIG. 23 have the same circuit configuration.

Therefore, these circuit regions may be achieved to have the same layoutas shown in FIG. 24. In FIG. 24, transistors QN21 to QN28, QN11 to QN18,select signals S10 to S13, /S10 to /S13 and low level power supply (Vss)lines in the circuit of FIG. 22 are shown, and in correspondence tothese, transistors QN51 to QN58, QP51 to QP58, select signals S20 to S23and high level power supply (Vdd) lines in the circuit of FIG. 12 areshown parenthesized. Although there is such a situation that therespective transistors corresponding to each other are of differentconductivity-types, it is possible to use the same layout for thesecircuits.

Vertically running wiring 410 in FIG. 24 are gate lines of transistorsthat serve as select lines and power supply lines of Vdd, Vss. These maybe simultaneously formed by patterning a polysilicon film. Since powersupply lines Vss, Vdd are merely required to be potentially fixed asnecessary for holding non-selected bit lines and word lines as being notfloating, it is not required that these are not very low resistive.Therefore, it is able to use for these lines the same polysilicon filmused for gate electrodes.

Although laterally running wirings 411 are shown by schematic straightlines, these are metal wirings which are contacted to sources and drainsof transistors. Contact portions 412 serve as to connect the metalwirings 411 to bit lines and word lines, to which the verticalinterconnection lines (i.e., contact plugs) 101 to 104 shown in FIG. 18are connected.

Bit lines and word lines in the above-described cell array arepreferably formed with a line/space of 1F/1F (F: minimum device-featuresize). These bit lines and word lines are connected while holding theline pitch to the read/write circuit 200 on the substrate as shown inFIG. 18. In this case, the metal wirings 411 shown in FIG. 24 are formedto have the same line/space of 1F/1F.

In contrast to this, transistors disposed on the way of the metalwirings 411 must have a large area necessary for supplying a requiredcurrent. In consideration to this view point, in FIG. 13, eachtransistor is formed to have a gate width of three pitches of the metalwirings 411.

When the transistor size and metal wire pitch are determined asabove-described, in order to effectively dispose the transistors, theselect signal lines (S10, /S10)(S20), (S11, /S11)(S21), (S12, /S12)(S22)and (S13, /S13)(S23) which are suffixed in accordance with an addressorder of 0, 1, 2 and 3 are arranged in such an order of (S10,/S10)(S20), (S12, /S12)(S22), (S11, /S11)(S21) and (S13, /S13)(S23).

As a result, between a transistor array of QN21(QN51), QN23(QN53)selected by the select signal line S10(S20) and a transistor array ofQN23(QN52), QN24(QN54) selected by the select signal line S11(S21),disposed is a transistor array of QN25(QN55), QN27(QN57) selected by theselect signal line S12(S22). By employing such the transistorarrangement, it is possible to dispose transistors with a large sizewithin a metal wiring area in which wirings are arranged at a smallpitch without idle spaces.

Next, referring to FIGS. 25 to 27, it will be explained that the bitlines, word lines and contact portions thereof to the read/write circuit200 are simultaneously formed by use of a dual damascene method.

FIG. 25 shows such a state that bit lines BL0 are formed on theinterlayer dielectric film 11 covering the substrate 10 on which theread/write circuit 200 has been formed. Simultaneous with the formationof these bit lines BL0, formed are contact plugs 103 a, 104 a by a dualdamascene process. These are used for connecting the word lines WL0, WL1to be stacked thereon to the read/write circuit 200. Although not shownin FIG. 25, other contact plugs for connecting end portions of the bitlines BL0 to the read/write circuit 200 are formed simultaneously withthe contact plugs 103 a, 104 a.

Then, as shown in FIG. 26, memory cells, each of which is constituted bya variable resistance element and a diode stacked each other, are formedon the bit lines BL0 at a predetermined pitch. Next, as shown in FIG.27, interlayer dielectric film 17 is deposited to cover the memory cellsMC, and then word lines WL0 are formed on the film 17 by a dualdamascene process. In this process, contact plugs 103 b and 104 b, whichare to be connected to the contact plugs 103 a and word lines WL1 to beformed next, respectively, are buried.

FIGS. 28A to 28C show the burying process of the word lines WL0 andcontact plugs 103 b, 104 b in detail in a cross sectional view along theword line WL0 direction. FIG. 28A shows such a state that the interlayerdielectric film 17 is deposited to cover the memory cells MC and thenplanarized.

Thereafter, as shown in FIG. 28B, wiring-burying trenches 501 are formedin the interlayer dielectric film 17 by an RIE (Reactive Ion Etching)process for word line burying so as to expose the upper ends of thememory cells MC. Further, contact holes 502 are formed at the positionswhere the contact plugs 103 a, 104 a have been buried so as to be deeperthan the trenches 501. Then, a wiring material metal layer is depositedand processed by a CMP (Chemical Mechanical Polishing) method. As aresult, as shown in FIG. 28C, the word lines WL0 and the contact plugs103 b, 104 b are simultaneously buried and formed.

Continuously, memory cell formations, interlayer dielectric filmdepositions, wiring and contact plug formations by use of the damascenemethod are periodically performed. By use of such processes, as shown inFIGS. 19 and 20, four-layered cell arrays may be stacked in such amanner that the bit lines and word lines of each layer is connected tothe read/write circuit on the substrate.

Having described the embodiments of the present invention, otherembodiments and variations will be apparent to those skilled in the art.Therefore, the invention should not be viewed as limited to thedisclosed embodiments but rather should be viewed as limited only by thespirit and scope of the appended claims.

Additional Embodiment

Another embodiment will be explained below. The memory device accordingto an additional embodiment explained below is a resistance changememory, which stores a high resistance state and a low resistance stateas information data as similar to the above-described programmableresistance memory, and is referred to as a phase change memory in a widesense. Therefore, the description in the above-described embodiment withreference to FIGS. 1 to 28C may be effective as it is in the embodimentdescribed below with the exception of the recording layer's material andrecording mechanism explained with reference to FIG. 1.

A recording layer constituting a variable resistance element in thisembodiment is formed of two, first and second, composite compoundlayers, which are stacked. The first compound layer contains at leasttwo types of cation elements represented by A_(x)M_(y)O_(z) while thesecond compound layer has at least one transition element and has acavity site capable of housing a cation moved from the first compoundlayer.

Explaining in detail, the first compound layer is a transition metaloxide expressed by A_(x)M_(y)O₄, which has, for example, a spinelstructure or a delafossite structure.

In this compound A_(x)M_(y)O₄, “A” is at least one element selected fromthe group consisting of Mg, Al, Mn, Fe, Co, Ni, and Zn; and “M” is atleast one element selected from the group consisting of V, Cr, Mn, Fe,Co and Ni.

It is required of “A” and “M” to be different from each other. Molarratios “x” and “y” are selected to satisfy 0.1≦x≦2.2 and 1.8≦y≦2,respectively.

With the above-described element “A”, ion radius necessary to maintain acertain crystal structure is optimized, and a sufficiently high ionconductivity may be achieved. By use of the above-described element “M”,it becomes easy to control the electron state in a crystal layer.

The first compound layer may be composed of another compound (transitionmetal oxide) A_(x)M_(y)O₃, which has, for example, an ilmenitestructure. In this compound A_(x)M_(y)O₃, “A” is at least one elementselected from the group consisting of Mg, Al, Mn, Fe, Co, Ni and Zn; and“M” is at least one element selected from the group consisting of V, Cr,Mn, Fe, Co and Ni.

It is required of “A” and “M” to be different from each other. Molarratios “x” and “y” are selected to satisfy 0.5≦x≦1.1 and 0.9≦y≦1,respectively.

With the above-described element “A”, ion radius necessary to maintain acertain crystal structure is optimized, and a sufficiently high ionconductivity may be achieved. By use of the above-described element “M”,it becomes easy to control the electron state in a crystal layer.

Further, the first compound layer may be composed of another compound(transition metal oxide) A_(x)M_(y)O₄ with another crystal structure,e.g., a wolframite structure. In this compound A_(x)M_(y)O₄, “A” is atleast one element selected from the group consisting of Mg, Al, Ga, Sb,Ti, Mn, Fe and Co; and “M” is at least one element selected from thegroup consisting of Cr, Mn, Mo and W.

It is required of “A” and “M” to be different from each other. Molarratios “x” and “y” are selected to satisfy 0.5≦x≦1.1 and 0.9≦y≦1,respectively.

With the above-described element “A”, ion radius necessary to maintain acertain crystal structure is optimized, and a sufficiently high ionconductivity may be achieved. By use of the above-described element “M”,it becomes easy to control the electron state in a crystal layer.

Crystalline structures employed as the first compound layer are asfollows:

-   -   Spinel structure    -   Cryptomelen structure    -   Ilmenite structure    -   Wolframite structure    -   Marokite structure    -   Hollandite structure    -   Heterolite structure    -   Ramsdelite structure    -   Olivine structure    -   Delafossite structure    -   α-NaFeO₂ structure    -   LiMoN₂ structure

The second compound layer is typically composed of Zn doped MnO₂ with aramsdelite structure. Further, the second compound layer may be composedof one of:

i. L_(x)MO₂

where, “L” is a cavity site, in which a cation element moved from thefirst compound is to be housed; “M” is at least one element selectedfrom Ti, Ge, Sn, V, Cr, Mn, Fe, Co, Ni, Nb, Ta, Mo, W, Re, Ru and Rh;and “O” is oxygen. Molar ratio “x” is selected to satisfy 1≦x≦2.

ii. L_(x)MO₃

where, “L” is a cavity site, in which a cation element moved from thefirst compound is to be housed; “M” is at least one element selectedfrom Ti, Ge, Sn, V, Cr, Mn, Fe, Co, Ni, Nb, Ta, Mo, W, Re, Ru and Rh;and “O” is oxygen. Molar ratios “x” is selected to satisfy 1≦x≦2.

iii. L_(x)MO₄

where, “L” is a cavity site, in which a cation element moved from thefirst compound is to be housed; “M” is at least one element selectedfrom Ti, Ge, Sn, V, Cr, Mn, Fe, Co, Ni, Nb, Ta, Mo, W, Re, Ru and Rh;and “O” is oxygen. Molar ratios “x” is selected to satisfy 1≦x≦2.

iv. L_(x)MPO_(y)

where, “L” is a cavity site, in which a cation element moved from thefirst compound is to be housed; “M” is at least one element selectedfrom Ti, Ge, Sn, V, Cr, Mn, Fe, Co, Ni, Nb, Ta, Mo, W, Re, Ru and Rh;“P” is phosphorous; and “O” is oxygen. Molar ratios “x” and “y” areselected to satisfy 0.3≦x≦3 and 4≦y≦6, respectively.

As the second compound layer, one of the following crystallinestructures may be employed.

-   -   Spinel structure    -   Hollandite structure    -   Ramsdelite structure    -   Anatase structure    -   Brookite structure    -   Pyrolusite structure    -   ReO₃ structure    -   MoO₃ structure    -   MoO_(1.5)PO₄ structure    -   TiO_(0.5)PO₄ structure    -   FePO₄ structure    -   βMnO₂    -   γMnO₂    -   λMnO₂    -   Perovskite structure

In FIGS. 33 to 41, there are shown combination examples of elementstogether with circles with respect to compound examples usable in thisembodiment. In addition to those shown in FIGS. 43-51, in thisembodiment, a two-element system transition metal oxide selected fromTiO_(x), CuO_(x), ZnO_(x), NiO_(x), MnO_(x), FeO_(x) and the like(where, ratio “x” is smaller than stoichiometric one) may also beemployed as the second compound.

A Fermi level of electrons in the first compound is set to be lower thanthat in the second compound. This is one of conditions required to causea state of the recording layer to have a reversible property. Any ofFermi levels used here is obtained as a value measured from a vacuumlevel.

Forming the recording layer as described above, the recording density ofPbpsi (Peta bits per square inch) class can be principally achieved, andfurther, low power consumption can also be achieved.

In this embodiment, preferable combinations of the first and secondcompounds are as follows:

-   -   a combination of spinel type compound (AM₂O₄) as the first        compound and ramsdelite type compound (A_(x)MO₂) as the second        compound;    -   a combination of Mn spinel type compound (ZnMn₂O₄) as the first        compound and Ti spinel type compound (ZnTi₂O₄) as the second        compound;    -   a combination of Mn spinel type compound (ZnMn₂O₄) as the first        compound and Al spinel type compound (ZnAl₂O₄) as the second        compound;    -   a combination of delafossite type compound (CuCoO₂) as the first        compound and ilmenite type compound (CoTiO₃) as the second        compound; and    -   a combination of delafossite type compound (CuCoO₂) as the first        compound and Ti spinel type compound (ZnTi₂O₄) as the second        compound.

FIG. 29 shows a variable resistance element (or unit) 500, in which arecording layer 502 has a stacked structure with a first compositecompound layer 502 a and a second composite compound layer 502 b.Recording layer 502 is sandwiched by electrode layers 501 and 503. Theupper electrode 503 serves as a protect layer.

The first compound layer 502 a allocated at the side of electrode 503has at least one type of transition element, and the second compoundlayer 502 b allocated at the side of electrode 501 has a cavity sitecapable of housing a positive ion moved from the first compound layer502 a.

In an initial state (i.e., reset state), the first compound layer 502 ais expressed by A_(x)M_(y)O_(z) while the second compound layer 502 b isin such a state that has a cavity site to be able to house a cationmoved from the first compound layer 502 a. This reset state is a highresistance state, i.e., stable state.

In a set state, the second compound layer 502 b is in such a state thata cation element moved from the first compound layer 502 a is housed inthe cavity site. At this time, the first compound layer 502 a is in astate, in which the compound is expressed by A_(x-u)M_(y)O_(z)(designating that element “A” descreased by “u” in correspondence to thecomponents moved to the second compound layer 502 b).

Here, for the purpose of simplification of the following explanation,the initial state (reset state) denotes such a state that the resistancevalue of the recording layer 502 is high while the set state denotessuch a state that the resistance value of the recording layer 502 islow.

For example, in case the second compound layer 502 b is formed ofMg²⁺Ti₂O₄ (or LTi⁴⁺O₄) and the first compound layer 502 a is formed ofLMn₂ ⁴⁺O₄ (or Mg²⁺Mn₂ ³⁺O₄), the resistance in the initial state (i.e.,reset state) is high and that in the set state is low.

Even if a device structure is identical to another, the resistance valueof the recording layer 502 changes in accordance with types of the firstand second compound layers 502 a and 502 b, so that the resistancevalues of the set and reset states may be freely set according to aproduct.

In FIG. 29, three types of small cycles in the recording layer 502denote cation elements (positive ion elements) while a large cycledenotes an anion element (negative ion element).

As shown in FIG. 30, the first and second compound layers 502 a and 502b constituting the recording layer 502 each may be stacked on two ormore multiple layers.

In the reset state, applying a voltage to the recording layer 502 insuch a manner that the electrodes 501 and 503 become cathode and anode,respectively, some of the positive ions in the first compound layer 502a move therein to be injected in part into the second compound layer 502b.

There are cavity sites in the second compound layer 502 b, which arecapable of housing the positive ions. Therefore, the positive ions movedfrom the first compound layer 502 a will be housed in the cavity sitesin the second compound layer 502 b.

As a result, the valence of the positive ion (transition element) in thefirst compound layer 502 a increases while that in the second compoundlayer 502 b decreases.

Assuming that the recording layer 502 is in a high resistance state(i.e., insulator state) as the initial state (reset state), as a resultof the positive ion movement as described above, the recording layer 502is set in a low resistance state (conductive state), i.e., set state.

By contrast, in a set state, when a voltage is applied to the recordinglayer 502 in such a manner that the electrodes 501 and 503 become anodeand cathode, respectively, some of the positive ions in the secondcompound layer 502 b move therein to be injected in part into the firstcompound layer 502 a.

The positive ions moved from the second compound layer 502 b will bestored in the first compound layer 502 a. As a result, the valence ofthe positive ion (transition element) in the second compound layer 502 bincreases while that in the first compound layer 502 a decreases.

Therefore, the recording layer 502 is reset to the initial state (highresistance state, i.e., insulator state) from the low resistance state.

As described above, the set/reset operation can be controlled by anorientation of the voltage applied to the recording layer 502(orientation of a voltage/current pulse).

The above-described “set” and “reset” are defined as: one of them is“write”; and the other is “erase”.

Data defined by the high resistance state and the low resistance statemay be read in such a manner as to supply a current pulse to therecording layer 502 and detect the resistance value thereof. It shouldbe noted here that it is required of the current pulse used at a readtime to be too small to cause resistance change of the recording layer502.

The set/reset operation can also be controlled by the following method.

The reset operation can also be performed by applying a voltage to therecording layer 502, thereby carrying a large current pulse in therecording layer 502. For example, the voltage is set in a manner thatelectrodes 501 and 503 serve as a cathode and an anode, respectively. Atthis time, setting the voltage to be lower than a level, at which ionsstart moving, or setting the pulse width of the voltage to be smallerthan a time length, in which ions start moving, joule heat is generatedin the recording layer 502.

As a result, part of the positive ions move in the second compound layer502 b to be diffused and drifted into the first compound layer 502 abecause the cathode side is lower in electrochemical energy. And thepositive ion elements moved from the second compound layer 502 b to thefirst compound layer 502 a are housed in the cavity sites therein.

Although electrons also move from the second compound layer 502 b to thefirst compound layer 502 a at this time, electron Fermi level in thefirst compound layer 502 a is lower than that in the second compoundlayer 502 b. Therefore, the total energy of the recording layer 502decreases, so that the reset state naturally advances.

The recording layer becomes in a high energy state after the setoperation has been completed. Therefore, Joule heat is not generated atthis time, and the set state can be continuously kept as it is. This isbecause that a so called ion transfer resistance works.

The valence of the element “A” moved from the first compound layer 502 aand housed in the second compound layer 502 b is responsible for thisworking. The fact that this element is bivalent has a very importantmeaning.

If the element “A” is a univalent element such as Li, a sufficient iontransfer resistance cannot be obtained in the set state, and positiveion elements immediately return from the second compound layer 502 b tothe first compound layer 502 a. In other words, it becomes impossible totake a sufficiently long retention time.

Therefore, it is preferable to provide an informationrecording/reproducing apparatus, in which the valence of the element “A”is bivalent.

In the meantime, after the reset operation is completed, an oxidizationagent is generated on the anode side. Thus, it is preferable to employ ahardly oxidized material (for example, electrically conductive oxide) asthe electrode 501.

It is preferable that electrically conductive oxide does not have ionconductivity. As an example of such oxide, the following materials canbe employed. The most preferable material from the view point ofcomprehensive performance considering a good electric conductivity isLaNiO₃.

MN

In the formula, “M” is at least one element selected from the groupconsisting of Ti, Zr, Hf, V, Nb and Ta; and “N” is nitrogen.

MO_(x)

In the formula, “M” is at least one element selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Ag,Hf, Ta, W, Re, Ir, Os and Pt; and “O” is oxygen. The molecular ratio “x”is set to satisfy 1≦x≦4.

AMO₃

In the formula, “A” is at least one element selected from the groupconsisting of K, Ca, Sr, Ba and Ln; “M” is at least one element selectedfrom the group consisting of Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd,Ag, Hf, Ta, Re, W, Ir, Os and Pt; and “O” is oxygen.

A₂MO₄

In the formula, “A” is at least one element selected from the groupconsisting of K, Ca, Sr, Ba and Ln; “M” is at least one element selectedfrom the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo,Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Os and Pt; and “O” is oxygen.

The reset operation may be carried out by promoting such a phenomenonthat the recording layer 502 is heated, and by accelerating the movementof the positive ions element housed in the cavity site of the secondcompound layer 502 b to the first compound layer 502 a.

Specifically, the recording layer 502 can be easily changed from the rowresistance state to the high resistance state by utilizing Joule-heatand its residual heat, which is generated by applying a mass currentpulse to the recording layer 502.

As described above, applying the mass current pulse to the recordinglayer 502, the resistance value of the recording layer 502 increases, sothat the reset operation is achieved.

Here, in order to achieve lower power consumption, it is important tofind out material, in which ion radius and moving path of the positiveion element are satisfied to make the positive ion moving withoutcausing a crystal destruction in the set operation.

FIG. 31 shows a preferable electrode structure of the memory element, inwhich a spinel type compound is used as at least part of the recordinglayer. Each of electrodes 501 and 503 is formed of a W film and a TiNfilm interposed between the W film and the recording layer 502.

In case the recording layer 502 has a spinel structure, it is preferableto employ (110)-oriented one. The W film may be formed as (110)-orientedone by selecting the deposition condition. Sequentially depositing TiNfilm, recording layer, TiN film and W film on the (110) W film, it ispossible to make the compound layer having a (110) spinel structure.

To efficiently carry out heating of the recording layer 502 in the resetoperation, for example as shown in FIG. 32A, it is preferable to providea heater layer 505 with a resistivity of 10⁻⁵/Ω-cm or more at the sideof upper electrode 503. Alternatively, such the heater layer 505 may bedisposed at the lower electrode 501 as shown in FIG. 32B. Further, asshown in FIG. 32C, heater layers 505 a and 505 b may be formed at thesides of the electrodes 501 and 503, respectively. Specifically, toeffectively heat the second compound layer 502 b at the reset time, theheater structure shown in FIG. 32B is desirable.

These heater layers 505, 505 a, 505 b may be preferably formed of a thinand high-resistive film of the same kind of compound as the recordinglayer 502. Explaining in detail, the heater layer 505 or 505 a disposedon the electrode 501 side is formed of the same kind of compound as thefirst compound layer 502 a; and the heater layer 505 or 505 b disposedon the electrode 503 side is formed of the same kind of compound as thesecond compound layer 502 b.

In addition, it is permissible that the TiN film shown in FIG. 31 servesas the heater layers described above.

Further, the first compound layer 502 a or the second compound layers502 b in the recording layer 502 may possess a plurality ofmicrostructures that have in common a continuous crystalline pathbetween the electrodes 501 and 503 in at least a part of the firstcompound layer 502 a or the second compound layer 502 b. The firstcompound layer 502 a or the second compound layer 502 b may consist of asingle-crystal film containing no grain boundary or a crystal film, thegrain size of which is smaller than the lateral size of a memory cell.

A polycrystalline or amorphous film may also be used if the firstcompound layer 502 a or the second compound layer 502 b which containsat least one columnar crystalline region that forms a continuouscrystalline path between the electrodes. Both the first and secondcompound layers 502 a and 502 b may be formed to be crystalline in atleast part of the device area. The first compound layer 502 a mayconsist of a single-crystalline film or a textured film within therecording layer 502. This embodiment remains effective regardless of theway in which the crystalline path between the electrode 501 and thesecond compound layer 502 b and between the electrode 503 and the firstcompound layer 502 a is formed. The first compound layer 502 a or thesecond compound layer 502 b may, for example, be deposited during devicemanufacture in an amorphous or nanocrystalline form, and the columnarcrystalline region is formed by local Joule heating during an initialforming stage of the device under a suitable bias current. As a result,the set/reset operation described above will be achieved by use of thecation movement in the crystalline regions of the first compound layer502 a.

1. A resistance change memory device comprising: a semiconductorsubstrate; at least one cell array, in which memory cells are arranged,formed above the semiconductor substrate, each the memory cell having astack structure of a variable resistance element and an access element,the variable resistance element storing a high resistance state or a lowresistance state in a non-volatile manner, the access element havingsuch an off-state resistance value in a certain voltage range that isten times or more as high as that in a select state; and a read/writecircuit formed on the semiconductor substrate as underlying the cellarray for data reading and data writing in communication with the cellarray, wherein the variable resistance element comprises a recordinglayer formed of a first composite compound expressed by A_(x)M_(y)O_(z)(where “A” and “M” are cation elements different from each other; “O”oxygen; and 0.5≦x≦1.5, 0.5≦y≦2.5 and 1.5≦z≦4.5) and a second compositecompound containing at least one transition element and a cavity sitefor housing a cation ion.
 2. The resistance change memory deviceaccording to claim 1, wherein the combination of the first compositecompound and the second composite compound is one selected from thegroup consisting of: a combination of spinel type compound (AM₂O₄) asthe first compound and ramsdelite type compound (A_(x)MO₂) as the secondcompound; a combination of Mn spinel type compound (ZnMn₂O₄) as thefirst compound and Ti spinel type compound (ZnTi₂O₄) as the secondcompound; a combination of Mn spinel type compound (ZnMn₂O₄) as thefirst composite compound and Al spinel type compound (ZnAl₂O₄) as thesecond composite compound; a combination of delafossite type compound(CuCoO₂) as the first composite compound and ilmenite type compound(CoTiO₃) as the second composite compound; and a combination ofdelafossite type compound (CuCoO₂) as the first composite compound andTi spinel type compound (ZnTi₂O₄) as the second composite compound. 3.The resistance change memory device according to claim 1, wherein theaccess element is a diode selected from a Zener diode, a PN junctiondiode and a Shottky diode.
 4. The resistance change memory deviceaccording to claim 3, wherein the read/write circuit is configured toapply such a first write voltage to a selected one of the memory cellsas to cause a diode thereof serving as the access element forward bias,thereby setting a variable resistance element thereof at a lowresistance state, and to apply such a second write voltage with apolarity opposite to the first write voltage to a selected one of thememory cell as to cause a diode thereof serving as the access elementbreakdown, thereby setting a variable resistance element thereof at ahigh resistance state.
 5. The resistance change memory device accordingto claim 4, wherein the read/write circuit is configured to apply such aread voltage lower than the first write voltage to a selected one of thememory cells as to make diode thereof forward-biased, thereby detectinga data state of a variable resistance element thereof.
 6. The resistancechange memory device according to claim 1, wherein the cell arraycomprises: a plurality of bit lines arranged in parallel with eachother; memory cells arranged on the respective bit lines at a certainpitch; and a plurality of word lines each formed to commonly connect theupper ends of the memory cells in such a direction as crossing the bitlines.
 7. The resistance change memory device according to claim 6,wherein the variable resistance element and the diode serving as theaccess element of each the memory cell are stacked between the bit linesand the word lines.
 8. The resistance change memory device according toclaim 7, wherein a plurality of cell arrays are stacked in such a mannerthat at least one of the bit lines and word lines are shared withadjacent two cell arrays.
 9. The resistance change memory deviceaccording to claim 8, further comprising: first and second verticalwirings disposed outside of first and second boundaries that define acell layout region of the cell arrays in the direction of the bit linesto connect the bit lines of the respective cell arrays to the read/writecircuit; and third vertical wirings disposed outside of one of third andfourth boundaries that define the cell layout region in the direction ofthe word lines to connect the word lines of the respective cell arraysto the read/write circuit.
 10. The resistance change memory deviceaccording to claim 9, wherein the first to third wirings are formed ofcontact plugs which are buried in an insulator layer formed to surroundthe cell arrays.
 11. The resistance change memory device according toclaim 9, wherein the read/write circuit comprises: a global bus regionhaving a plurality of data lines to which read data are transferred anda plurality of write pulse signal lines for transferring write pulsesignals to the bit lines, the data lines and the write pulse signallines being so disposed as to cross a central portion of the cell layoutregion in the direction of the bit lines; first and second bit lineselect circuits disposed along the first and second boundaries of thecell layout region, respectively, to which the respective bit lines ofneighboring two cell arrays are connected; first and second sense amparrays for sensing data of bit lines selected by the first and secondbit line select circuits, respectively, the first and second sense amparrays being disposed between the first, second bit line select circuitsand the global bus region, respectively; a word line select circuitdisposed along one of the third and fourth boundaries of the cell layoutregion, to which shared word lines of the neighboring two cell arraysare connected; and a write circuit disposed along the other of the thirdand fourth boundaries of the cell layout region for generating the writepulse signals supplied to the write pulse signal lines.
 12. Theresistance change memory device according to claim 11, wherein theshared word lines are simultaneously activated for a certain range whichis selected by the word line select circuit, and the respective bitlines of the neighboring two cell arrays are simultaneously selected forthe respective certain ranges which are selected by the first and secondbit line select circuits, respectively, thereby simultaneously accessingto the respective plural memory cells in the neighboring two cellarrays.
 13. The resistance change memory device according to claim 12,wherein the first and second sense amp arrays have sense amps forsimultaneously sensing data of the respective plural memory cells whichare simultaneously selected in the neighboring two cell arrays, senseddata of which are simultaneously transferred to the data lines in theglobal bus region.
 14. The resistance change memory device according toclaim 12, wherein the write circuit is configured to simultaneouslyoutput write pulse signals, which are to be transferred to therespective plural bit lines simultaneously selected in the neighboringtwo cell arrays, to the write pulse signal lines in the global busregion.
 15. The resistance change memory device according to claim 11,wherein neighboring two memory cells in each the cell array constitute apair cell for storing complementary data, one of which is a highresistance state and the other is a low resistance state, and whereineach of the first and second sense amp arrays comprises differentialtype current sensing amplifiers arranged therein, each of the currentsensing amplifiers being connected to a bit line pair to which the paircell is connected for sensing a current difference due to thecomplementary data.
 16. The resistance change memory device according toclaim 8, wherein neighboring two memory cells in each the plurality ofcell arrays constitute a pair cell for storing complementary data, oneof which is a high resistance state, and the other is a low resistancestate, and wherein the complementary data of the pair cell are read outto a bit line pair as one bit of data.
 17. The resistance change memorydevice according to claim 16, wherein two memory cells constituting thepair cell are laterally neighboring in each of the plurality of cellarrays in such a manner that anodes of diodes thereof are commonlyconnected to one of the word lines and anodes of variable resistanceelements thereof are connected to a pair of bit lines.
 18. Theresistance change memory device according to claim 17, wherein the paircell is selected in such a condition that another bit line is disposedbetween the pair of bit lines to which the complementary data are readout.
 19. The resistance change memory device according to claim 16,wherein two memory cells constituting the pair cell are verticallyneighboring between neighboring two cell arrays in the plurality of cellarrays in such a manner that anodes of diodes thereof are commonlyconnected to one of the word lines shared by the two cell arrays, andanodes of variable resistance elements thereof are connected to bitlines disposed at the two cell arrays, respectively.
 20. The resistancechange memory device according to claim 7, wherein the read/writecircuit is configured to apply such a first write voltage to a selectedone of the memory cells through a selected bit line and a selected wordline as to make diode thereof forward-biased, thereby setting a variableresistance element thereof at a low resistance state, and to apply sucha second write voltage with a polarity opposite to the first writevoltage to a selected one of the memory cells through a selected bitline and a selected word line as to make diode thereof breakdown,thereby setting a variable resistance element thereof at a highresistance state.
 21. The resistance change memory device according toclaim 20, wherein the read/write circuit is configured to apply such aread voltage lower than the first write voltage to a selected one of thememory cells through a selected bit line and a selected word line as tomake diode thereof forward-biased, thereby detecting a data state of avariable resistance element thereof.
 22. The resistance change memorydevice according to claim 21, wherein the read/write circuit isconfigured to apply such a hold voltage between the bit lines and wordlines in a non-select state as to keep the diodes of the memory cells ata high impedance off-state with a reverse bias.